Remove redundant "value of o11y" content from learning paths

## Problem

Several learning paths include a generic "value of observability" section (explaining what observability is / why it matters in general terms). This content is redundant across the affected LPs and should be removed.

## Affected learning paths

- `monitor-aws-resources-lj`
- `send-traces-alloy-lp`
- `send-logs-alloy-loki-lj`
- `prom-remote-write-lj`
- `windows-integration-lp`
- `macos-integration-lj`
- `kubernetes-lp`
- `prometheus-lj`
- `monitor-azure-resources-lj`
- `linux-server-integration-lj`

(Found via `grep -rli "value of o11y\|value of observability"` across the repo — worth re-checking for any additional matches at implementation time.)

## Special case: `linux-server-integration-lj`

Unlike the other LPs, `linux-server-integration-lj/business-value/content.json` combines the generic "value of observability" content with LP-specific content ("## The value of the Linux server integration" section, including its own embedded video) in a single page.

For comparison, `kubernetes-lp` already splits this into two separate pages — a generic `business-value/` page and an LP-specific `business-value-k8s/` page — so removing the generic one there is a clean deletion.

For `linux-server-integration-lj`, the LP-specific "value of the Linux server integration" section (and video) must **not** be deleted along with the generic content — it needs to be preserved and moved up to the top-level page (`linux-server-integration-lj/content.json`) before the `business-value/` page (or the redundant portion of it) is removed.

## Acceptance criteria

- [ ] Generic "value of observability" content removed from all LPs listed above
- [ ] For `linux-server-integration-lj`: LP-specific "value of the Linux server integration" content (including video) relocated to the top-level `content.json` before removal of the redundant section
- [ ] Manifests/navigation updated for any LP where a whole page (not just a section) is removed
- [ ] Spot-check remaining LPs for any other instances of this redundant content not caught by the initial grep

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